1. Field of the Invention
The present invention relates to a module structure using flat cells, each flat cell having a structure in which a laminate film of polymer-metal composite is used as a cell outer case and in which a periphery of the cell outer case is joined by thermal fusion to house and seal an electric power generating element formed by stacking or winding a positive electrode plate, a separator and a negative electrode plate.
2. Description of the Related Art
Recently, the air pollution caused by an exhaust gas from vehicles has become a global problem. In such a context, electric vehicles, which use an electric power as a motive power source, and hybrid cars, which are run by the combination of an engine and a motor, have been attracting attention. Correspondingly, the development of a battery having a high energy density and a high output density to be mounted on these hybrid cars has an important place industrially. As a configuration of a battery for such use, there is a configuration in which a wound electric power generating element is housed within a cylindrical case. In another configuration, a wound electric power generating element or an electric power generating element, which stacks planar electrodes and a separator, is housed within a flat case.
Since these cylindrical or flat cases are required to have enhanced strength, it is necessary to form these cases as metal cans. Therefore, there is a problem that the reduction of weight is difficult. Thus, as means of reducing the weight of a battery as well as obtaining a higher energy density and a higher output, the prior art as described in Japanese Patent Application Laid-Open No. 11-224652 (1999) is cited. In this conventional technology, a structure of a battery using a laminate film as an outer case, a periphery of which is sealed by thermal fusion to close the outer case hermetically, has been proposed.
However in such a battery using a laminate sheet as a cell outer case, because the laminate film has poor rigidity, the application of an external force easily deforms the battery. Excessive deformation resulting from the external force breaks the internal structure of the battery, causing internal short-circuiting. Moreover, the thermally fused portion of the outer periphery of the battery is particularly easily deformed. Therefore, there is a possibility that the sealability may be impaired by the deformation due to the application of an external force or an increase in internal pressure due to an increase in the temperature of the battery.
Furthermore, since the battery using a laminate film as an outer case is inferior to that using a metal can from the view point of the ability to compress the electric power generating element housed within the battery case, a distance between a positive electrode plate and a negative electrode plate becomes uneven, making it difficult to exert the electric power generating ability. Therefore, it is necessary to equalize a distance between the positive electrode plate and the negative electrode plate by some means.
Thus, as a measure against such deformation of the battery, in particular, deformation of the outer periphery of the battery, Japanese Patent Application Laid-Open No. 2000-306556 discloses a battery in which a frame is attached to an outer periphery of the battery. In this conventional technology, with regard to deformation, the outer periphery of the battery can be maintained reliably. However, since the frame is adhered only to the outer periphery of the battery, a distance between a positive electrode plate and a negative electrode plate may become uneven. As a result, there arises a problem in that the high-current discharge performance cannot be fully exerted when the battery is mounted onto an electric vehicle or a hybrid car.
The present invention has been made in consideration of the above problems. It is an object of the present invention to provide a battery module capable of enhancing the reliability of the sealability of a cell so as to ensure the charge/discharge performance at a high current, in a cell using a laminate film of polymer-metal composite as a cell outer case.
To achieve the object described above, the present invention provides a battery module, comprising: a flat cell comprising: a laminate film constituted by a polymer-metal composite, the laminate film being a cell outer case; an electric power generating element formed by stacking or winding a positive electrode plate, a separator and a negative electrode plate; lead terminals for flowing and receiving current to/from the electric power generating element; a cell outer case junction part formed by partially or completely covering the electric power generating element with the laminate film, and by sealing the laminate film by thermal fusion; a cell assembly formed by collecting a plurality of the flat cells; and a pair of planar supports for interposing the cell assembly from a direction opposed to planes of the flat cells; wherein rib-shaped protrusions respectively including electrical conductors for electrically connecting the lead terminals of a plurality of the flat cells are provided on at least one of the planar supports, the rib-shaped protrusions being held on the planar support at predetermined intervals, and the planar supports pressing and supporting the cell assembly.